1. Field of the Invention
The present invention relates to a beam extraction slit structure and an ion source.
2. Description of the Related Art
One of the standard processes in semiconductor manufacturing is to implant ions in a semiconductor wafer for the purpose of modifying the conductivity or modifying the crystal structure of a semiconductor wafer. Devices used in this step are generally called ion implanters.
Indirectly heated cathode ion sources are known to be used in ion implanters. An indirectly heated cathode ion source is configured to heat a filament by a direct current so as to generate thermoelectrons, which heat the cathode. The thermoelectrons generated from the heated cathode are accelerated in an arc chamber and collide with source gas molecules in the arc chamber, thereby ionizing atoms included in the source gas molecules.
The electric field produced at the beam extraction slit of the arc chamber in accordance with the voltage applied across the extraction electrode and the beam extraction slit extracts a beam from the ion source. The electric field extracts ions from the plasma in the arc chamber, guiding the ions through the extraction slit as an ion beam. The interface of the plasma is formed at a position where ions are extracted from the plasma as a beam. The interface is called a plasma meniscus. The position and shape of the plasma meniscus varies greatly depending on the plasma density or electric field intensity. For example, when the plasma density is decreased, the plasma meniscus recedes toward the plasma. Conversely, when the plasma density is increased, the plasma meniscus advances toward the extraction electrode. The position and shape of the plasma meniscus affect properties of the ion beam extracted. The beam properties affect the efficiency of beam transportation in the ion implanter, and, ultimately, the productivity of the implanter.